Create GitHub Action that checks the solution is compilable.

[Issung]

We don't have any tests at the moment but at the very least we want to make sure that before any work gets merged it atleast compiles OK. This is a good intro lession to the concept of CICD.

Note because GChan is .NET Framework and not .NET Core we will need to use a Windows builder, not Linux.
https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-net

[Issung]

In order to save processing minutes make the action only run on branches that have a PR created.